Experts say the data reflect not just worsening public health but better medicines for chronic conditions and more aggressive treatment by doctors. For example, more people are now taking blood pressure and cholesterol-lowering medicines because they need them, said Dr. Daniel W. Jones, president of the American Heart Association.

In addition, there is the pharmaceutical industry's relentless advertising. With those factors unlikely to change, doctors say the proportion of Americans on chronic medications can only grow.

"Unless we do things to change the way we're managing health in this country ... things will get worse instead of getting better," predicted Jones, a heart specialist and dean of the University of Mississippi's medical school.

Americans buy much more medicine per person than any other country. But it was unclear how their prescriptions compare to those of insured people elsewhere. Comparable data were not available for Europe, for instance.